The Launceston 31-year-old had already sustained two dropped chains and a puncture before crashing on the descent of the Vista Chinesa circuit in Rio de Janeiro, when in medal contention 35 kilometres from the end of the 237km race.

He also sustained contusions and bruising and immediately withdrew from Wednesday's time trial.

"We were away with a small group on the descent and on one of the corners I came around and there was a guy on the road who crashed and I had nowhere to go,” explained Porte, who was only denied a podium finish in last month's Tour de France by an untimely puncture.

"It was fortunate a tree stopped me from going over the side.

“I’m bruised and battered and sore and I'm disappointed but lucky I’m not worse off.

“I hit it with a fair bit of speed and it’s really disappointing because the guys were good all day looking after me and then for this to happen, it hurts."

Speaking after being released from Vitoria Hospital in Barra, Porte added: “I’m definitely out of the time trial. I won’t be able to ride for at least ten days, my arm's in a sling and I can’t really move my arm.”

Porte made sure to call both his wife Gemma, who is in Rio, and his mum Penny back in Launceston to tell them he would be okay.

"Obviously it’s hard on Gemma when she hears I’ve crashed, I guess it’s part of being a cyclists’ wife,” he said.

"It’s just so disappointing to not be able to do the time trial and not be able to finish the race today."

Australian coach Brad McGee said on the finish line: "Richie actually made the joke as he was laying there in the gutter in a lot of pain, 'Macca', he said, 'I don't think I'm in for the time trial'.

"He's in good spirits but obviously in a lot of pain and we'll have to check him out. There are definitely a few breaks in there somewhere.

"He was definitely right where we wanted him. He had already recovered from a couple of incidents, but he was in a good mindset, and the boys today did exactly what he needed."

Hobart's Scott Bowden had done his job to stay with the Australian team leader but subsequently withdrew from the race to focus on the mountain biking.

The 21-year-old was proud of his debut Olympic performance.

"I think the process, the plan we had geared around Richie for the race, we did everything we could," Bowden said.

"For me it was unreal, expectations before this race, it was everything and more."

Italy's Tour de France winner Vincenzo Nibali and Porte's former Sky teammate Geraint Thomas, of Great Britain, also crashed on the same descent.

The race was eventually won by Porte's BMC teammate Greg Van Avermaet, of Belgium.

Hobart's four-time Olympian Kerry Hore said she was satisfied with her quad scull crew's second place in its heat at Lagoa Rodrigo de Freitas.

The Australian crew, also including young Queenslanders Madeleine Edmunds and Jessica Hall and Victorian Jen Cleary, finished second in 6:37.43, 1.95 seconds behind Ukraine who qualified straight into the final.

"It was really challenging but we handled the conditions really well and put down a solid performance," said Hore, 35.

"Obviously we would've liked to have won and gone straight through but we have a chance to have another hit out.

"We're getting more and more comfortable with the conditions as we train and race and I was really happy with how we handled it today and one more hit out will not be a disadvantage for sure, I think it will help us.

"We know each other fairly well but it was good to know we were able to stay calm under that pressure and in those conditions."

Germany also qualified directly having set a blistering best time of 6:30.86 in the other heat at Lagoa Rodrigo de Freitas.

Hore's crew will face repechage on Monday seeking to reach Wednesday's final.

Eddie Ockenden and Tim Deavin both started on field as the Kookaburras made a nervy but ultimately successful start to their Olympic campaign.

The Tasmanians played their 279th and 133rd international matches respectively as Australia survived a fight back to beat trains-Tasman rivals New Zealand 2-1 thanks to a penalty corner from Chris Ciriello in the eighth minute and a 23rd-minute field goal from Matt Gohdes.

Graham Reid's team have no let-up as they face a second game in as many days on Sunday against their Beijing Olympic conquerors Spain.